FIG. 15 shows headphones 10 of a typical conventional example (FIG. 15A is a front view, and FIG. 15B is a side view). Usually, the headphones 10 have a substantially C-shaped headband 11 arranged along the top of the user's head, and at both ends of the headband 11, a pair of right and left headphone units 13 are supported via hanger members 12.
Each of the headphone units 13 has a housing 13a incorporating an electroacoustic transducer, not shown, and on the sound emission surface side of the housing 13a, an ear pad 13b formed of an elastic material is provided. Each of the hanger members 12 is provided with arms 12a formed into inverse Y forked shape as described in, for example, Patent Document 1 (Japanese Patent Application Publication No. H09-182183).
As shown in an enlarged sectional view of FIG. 16, connecting pins 14 are provided coaxially in the end portions of the arms 12a. By inserting the connecting pins 14 into engagement holes on the housing 13a side, the headphone unit 13 is held on the hanger member 12 so as to be turnable with the rotation axis of the connecting pins 14 being the center.
As the headband 11, an elastic band plate of, for example, a metal is used. The headband 11 is formed substantially into a C shape with a predetermined curvature so that the width between the both ends thereof is narrower than the average head width of the ordinary adult. When the headphones 10 are used, the user opens out the headband 11 in the right and left direction in FIG. 15A, and wears the headphone units 13 by holding them to his/her ears.
Thus, when the headphones 10 are worn, the headband 11 is curvedly deformed so that the radius of curvature thereof increases, by which an urging force (restoring force) is generated in the headband 11 in the direction such that the initial radius of curvature is restored (the direction such that the radius of curvature decreases).
This urging force of the headband 11 is determined by the difference between the initial radius of curvature and the radius of curvature at the time when the headphones are worn and the physical properties such as shape and material of the headband 11. Therefore, the headband 11 is designed so as to give a good sense of wearing to the user having the average head width.
Actually, however, the width of the human head varies considerably. When FIG. 17A shows a person having a narrow head width, FIG. 17B shows a person having an average head width, and FIG. 17C shows a person having a wide head width, it has been known from actual measurement that there is a difference of about ±2 cm with respect to the average head width.
As described before, the headphones 10 are designed so as to give a good sense of wearing to the user by using the person having an average head width shown in FIG. 17B as the reference. In this case, the design standard plane for determining the urging force of the headband 11 is a contact plane 15 of the headphone unit 13 for the head having the average width.
On the other hand, as shown in FIG. 17A, a contact plane 16 of the headphone unit 13 for the person having a head width narrower than the average is narrower than the contact plane 15 shown in FIG. 17B, so that the urging force of the headband 11 at the time when the headphones 10 are worn is weaker than the design value.
Also, as shown in FIG. 17C, a contact plane 17 of the headphone unit 13 for the person having a head width wider than the average is wider than the contact plane 15 shown in FIG. 17B, so that the urging force of the headband 11 at the time when the headphones 10 are worn is weaker than the design value.
In both cases, a good sense of wearing cannot be obtained because of the urging force different from the design value. In addition, in the case where the urging force is weak, the headphone unit 13 is not sufficiently pressed onto the ear, which presents a problem in that sound leakage occurs, and hence the propagation of sound pressure from the headphone unit to the ear is insufficient.
Also, in the case where the urging force is strong, though sound leakage does not occur and hence the propagation of sound pressure from the headphone unit 13 to the ear is sufficient, but long-term wearing sometimes causes a physical pain to the user.
Accordingly, an object of the present invention is to provide headphones in which a substantially constant urging force can always be obtained without being influenced by a difference in width and shape of the user's head.